Double walled perforated oil well liner



March 20, 1962 D. w. FETHER DOUBLE WALLED PERFORATED OIL WELL LINER Filed Jan. 19, 1959 FY 5 mm T a y a @MX M 0 J22 \IQ m yl a w A M M 2 2 0 fly B FIG-4 F1 0. 5'

United States Patent 3,925,914 Patented Mar. 20, 1962 hee 3,025,914 DOUBLE WALLED PERFORATED GIL WELL LINER Donald W. Fether, Los Angeles, Calif. (999 4th St, Saticoy, Calif.) Filed Jan. 19, 1959, Ser. No. 787,525 5 Claims. (Cl. 166-235) This invention relates to perforated well pipe, and this application is a continuation-in-part of my applications: Serial No. 467,436, filed November 8, 1954, for Well Screen, now abandoned; Serial No. 532,442, filed September 6, 1955, for Perforated Pipe Structure, now Patent No. 2,872,984, granted February 10, 1959; and Serial No. 551,251, filed December 6, 1955, for Liner Pipe Construction for Wells, now abandoned.

Included in the objects of this invention are:

' First, to provide a perforated well pipe having an inner and an outer wall construction wherein the perforations in the inner wall have substantially greater effective area per unit length than the perforations in the outer wall, thereby to cause a substantial reduction in the rate of flow between the outer and inner walls so as to reduce the silt and sand carrying power of incoming fluids, particularly when the fluids are subjected to gas drive surges.

Second, to provide a perforated well pipe wherein the relationship between the average radial spacing of the inner and outer walls and the distance between perforations is such as to provide a maximum drag on the sand or silt without causing plugging of the annulus between the walls.

Third, to provide a perforated well pipe wherein the width of the perforations, whether in the form of slots or circular openings, is not less than one-half of the effective wall thickness of the pipe wall, and wherein the total peripheral area of the perforations in any transverse plane does not exceed twenty percent of the pipe wall circumference.

With the above and other objects in view, as may ap pear hereinafter, reference is directed to the accompanying drawings in which:

FIGURE 1 is a fragmentary, longitudinal, sectional view of the perforated well pipe taken through 1-1 of FIGURE 2;

FIGURE 2 is an enlarged, transverse, sectional view through 22 of FIGURE 1;

FIGURE 3 is a fragmentary, sectional view through 33 of FIGURE 2;

FIGURE 4 is a fragmentary, sectional view similar to FIGURE 3, showing a modified form of the perforated well pipe;

FIGURE 5 is another sectional view similar to FIGURE 3, showing a further modified form of the perforated well pipe;

FIGURE 6 is an enlarged, fragmentary, sectional view showing a modified form of perforation which may be employed.

Reference is first directed to FIGURES 1, 2, and 3. In the construction here illustrated, the perforated pipe includes a cylindrical inner pipe 1 and an annular undulated or corrugated outer pipe 2.

The outer pipe 2 comprises a series of upwardly expanding troweling cones 3 and downwardly expanding fluid inlet cones 4, the troweling and inlet cones being joined alternately at their major diametered ends and minor diametered ends. The outer pipe 2 may be a continuous length involving a series of troweling cones and fluid inlet cones; and may be formed by inserting a cylindrical pipe within a form corresponding in contour to the intended outer surface of the outer pipe, then applying internal pressure to swell the pipe, and thus provide integrally connected cones 3 and 4.

The outer pipe 2 may extend the length of the inner pipe 1 or may be made in shorter sections, preferably terminating at the minor diarnetered ends of the cones so that a series of the outer pipes may be fitted on the inner pipe in abutting relation and joined to each other as well as to the inner pipe by means of welds 5. At their junctures, the major diametered ends of the cones may flatten to form short cylindrical lands 6, and similarly the junctures of the major 'diametered ends of the cones may form cylindrical lands 7 of short axial length.

Each fluid inlet cone 4 of the outer pipe 2 is provided with a ring of axially extending slots 8. The inner pipe 1 is provided within each unit length, represented by the distance between a pair of lands 6, with two rings of axially extending slots 9 and 10. The upper set of slots 9 may be located in a plane coinciding substantially with the slots 8. However, they are circumferentially displaced, as shown best in FIGURE 2, so that there is no direct line of communication through the slots 8 and 9.

The width of each slot 8, 9, or 10 should be not less than one-half the thickness of the pipe; that is, the width A should be not less than one-half the thickness of B, as shown in FIGURE 2. The peripheral distance between the centers of the slots 9 or 10 should not be greater than five times the average radial distance between the inner and outer pipes; that is, the distance C should not be greater than live times the average distance D, as shown in FIGURE 2. As shown in FIGS. 1 and 2, the radial dimension, in any transverse plane, of each of the annular chambers defined by the inner and outer pipes 1 and 2 is less than the internal radius of the inner pipe in such plane.

The total area of the slots 9 and 10 within each unit length of inner pipe should be at least one and one-half times the total area of the slots 8. In the construction shown, assuming that the slots are equal in width, the combined area of slots 9 and It) is twice the combined area of slots 8 per unit length of pipe.

If it is desired to provide a narrower slot, narrower than one-half the maximum thickness of the pipe, this may be done, as shown in FIGURE 6, by providing an external recess 11 having an outwardly diverging slope greater than the angle of repose of the sand or silt, or be arranged in the form of a wide channel, as indicated by 11a. In either case, the effective thickness of the pipe is B, and the width A of the slot 12 may be correspondingly narrower than the slots 8, 9, or 10 of the first described structure.

Reference is now directed to FIGURE 4. The construction here shown corresponds to the disclosure in my copending application, Serial No. 532,442. In this construction, the inner pipe 1 is provided with a series of collars 13, each in the form of a pair of cone frustums joined by their larger ends to form troweling cones 14 and fluid inlet cones 15. In this construction, two or more rings of perforations 16' are provided in the inlet cones 15.

The inner pipe is provided with rings of perforations 17. The series of collars 13 are joined by their smaller ends to the inner pipe by welds 18. The same rules as set forth in the first described structure apply to the construction shown in FIGURE 4; that is, the diameter of the perforations 16 and 17 should be not less than onehalf the wall thickness of the collar 13 or the pipe 1, as the case may be.

The circumferential spacing of the perforations 17 should not be greater than five times the average radial spacing betweenthe inner pipe and collars, and the total area of the perforations per unit of pipe should be at least one and one-half times the total area of perforations in the corresponding collar. In the construction illustrated,

3 the ratio of total area perforations 17 to total area perforations 16 is two to one.

Reference is now directed to the embodiment of the invention shown in FIGURE 5. This construction corresponds to the construction disclosed in my copending application, Serial No. 551,251. In this construction, an outer pipe 28 comprises a series of cylindrical sections of uniform diameter. The sections are spaced from the inner pipe by a series of annular rings 19 joined to the exterior of the inner pipe by welds 20. Welds 21 oin the outer pipe sections to the rings 19 and to each other in end-to-end relation.

In this construction, each outer pipe section is provided with a series of perforations 22 Whereas the inner pipe is provided with sets of perforations 23. The perforations 22 are shown as more numerous but of shorter length than the perforations 23. However, the relationship between the perforations inherent in the previously described structures is maintained; that is, the minor dimension of the perforations 22 and 23 are at least onehalf the effective wall thickness of the outer pipe sections 28 and the inner pipe 1. Also the circumferential distanee of the perforations 23 are similar to those shown in FIGURE 2; that is, their circumferential spacing is not more than five times the average radial distance between the inner pipe 1 and outer pipe sections 28.

Still further, the total area of the perforations 23 per unit length of pipe is not less than one and one-half times the total area of the perforations 22 although the perforations 22 are shown as more numerous. While in FIG- URE the perforations 23 are shown as in radial align- 'ment with perforations 22, it is preferred that they be cirpurnfer'entially displaced in the manner shown in FIG- URE 2-. 7

With respect to the constructions shown in FIGURES l to 3 and/1, the provision of the undulating outer pipe or a plurality of collars establishes a series of upwardly converging troweling surfaces and protects the perforations 3 or 16 from becoming clogged with mud or other coating, which lines the interior of the surrounding well casing in the upper portion of the well bore and also lines the open formation in the lower portion of the well bore, during the process of lowering the perforated pipe into a well bore.

It should be observed that because of the misalignment of the perforations and the particular relation between the radius of the aiflnulus D to the spacing C, a limited quantity of sand and fines is permitted to accumulate. Howevenpacking of the sand and fines sufficient to impair flow is prevented. That is, before excessive accumulation and consequent packing of sand and fines occurs, the excess passes through the inner perforations. This is evidenced by the fact that during an initial period of use sand and fines present in the immediately surrounding formation enter the inner pipe and are removed by pumping or bailing. After this initial period, a condition of equilibrium is reached in which inflow of sand and fines substantially ceases; however, there is no evidence of plugging or packing of sand and fines in the annulus between the pipes.

The presence of loose sand and fines tends to distribute the flow of fluid, and the greater area of the inner perforations reduces the velocity of the fluid so that its carrying power, that is, its ability to carry sand and fines is materially reduced. In fact, it has been established that the carrying power of a moving fluid increases as the sixth power of its velocity.

However, as pointed out previously, should the sand and fines tend to reduce the effective flow area Within the annulus between the pipes to the point that flow velocities are increased through the sand and fines, the increased carrying power of the fluid due to its increased velocity carries the excess sands and fines through the inner perforations and restores the optimum condition. If the distance through the sand and fines from the outer perforations to the inner perforations were too great, the sands and fines would tend to pack; hence, the relationship of the radius D and the perforation spacing C is important.

It should be noted that the total number of perforations 5 is such that flow through any given perforation is relatively slow, even though the Well may produce a large number of barrels of liquid per day. Thus, it is highly desirable to ensure a relatively low rate of flow through a maximum number of perforations and thus reduce the ability of the moving fluids to carry sand and fines.

It should be observed that the outer pipe or series of collars, as the case may be, need not be Welded to the inner pipe at frequent intervals, in fact, may be joined only at the ends of the inner pipe.

While particular embodiments of this invention have been shown and described, it is not intended to limit the same to the exact details of the constructions set forth, and it embraces such changes, modifications, and equivalents of the parts and their formation andv arrangement as come within the purview of the appended claims.

What is claimed is:

1. A double walled, perforated liner for oil Wells, comprising:

(a) inner liner means;

(b) outer liner means concentric with said inner liner means;

(6) said inner and outer liner means providing therebetween a plurality of axially spaced, annular chambers each having axially spaced ends and each having concentric, perforated inner and outer walls of circular .cross section in transverse planes;

(d) the total area of the perforations in said inner wall of each of said annular chambers being greater by at least fifty percent than the total area of the perforations in said outer wall thereof;

(e) the circumferential distance between the centers of the perforations in said inner Wall of each of said annular chambers being not greater than about five times the average radial distance between said inner and outer walls; and

(f) the smallest dimension of each of said perforations being not less than one-half the etfectivethickness of the said wall in which it is formed.

2. A double walled, perforated liner for oil wells, comprising:

(a) inner liner means;

(b) outer liner means concentric with said inner liner means;

(0) said inner and outer liner means providing therebetween a plurality of axially spaced, annular chambers each having axially spaced ends and each having concentric, perforated inner and outer Walls of circular cross section in transverse planes;

(d) the total area of the perforations in said inner wall of each of said annular chambers being greater by at least fifty percent than the total area of the perforations in said outer wall thereof;

(2) the circumferential distance between the centers of the perforations in said inner Wall of each of said annular chambers being not greater than about five times the average radial distance between said inner and outer walls;

(f) the smallest dimension of each of said perforations being not less than one-half the effective thickness of the said wall in which it is formed; and

(g) said perforations in said inner wall of eachrof said annular chambers occupying not more than twenty percent of the circumference of said inner wall in any transverse plane.

70 3. A double walled, perforated liner for oil wells, comprising:

(a) inner liner means;

(b) outer liner means concentric with said inner liner means;

75 (c) said inner and outer liner means providing therebetween a plurality of axially spaced, annular chambers each having axially spaced ends and each having concentric, perforated inner and outer walls of circular cross section in transverse planes;

((1) the total area of the perforations in said inner wall of each of said annular chambers being greater by "at least fifty percent than the total area of the perforations in said outer wall thereof;

(e) the circumferential distance between the centers of the perforations in said inner wall of each of said annular chambers being not greater than about five times the average radial distance between said inner and outer walls;

(1) the smallest dimension of each of said perforations being not less than one-half the effective thickness of the said wall in which it is formed;

(g) said perforations in said inner wall of each of said annular chambers occupying not more than twenty percent of the circumference of said inner wall in any transverse plane; and

(h) the radial dimension of each of said annular chambers in any transverse plane being less than the internal radius of said inner wall in such plane.

References Cited in the file of this patent UNITED STATES PATENTS 49,418 Koon Aug. 15, 1865 140,665 Wilson July 8, 1873 2,257,344 Maloney Sept. 30, 1941 2,681,111 Thompson June 15, 1954 FOREIGN PATENTS 813,005 France Feb. 15, 1937 

